Mozilla and Opera have mocked Microsoft's use of the term "native HTML5" to describe IE9 and the upcoming IE10 as an oxymoron, an attempt to hijack an open standard and a marketing ploy.

Mozilla and Opera have mocked rival Microsoft's use of the term "native HTML5" to describe Internet Explorer 9 (IE9) and the in-development IE10 as an oxymoron, an attempt to hijack an open standard and a marketing ploy.

On Tuesday, Microsoft's Dean Hachamovitch, the executive who runs the IE group, used the term several times during a keynote at MIX, the company's annual web developers conference and in an accompanying post on the IE blog.

Although Hachamovitch didn't define "native HTML5", he came closest in the blog .

"Websites and HTML5 run best when they run natively on a browser optimised for the operating system on your device," said Hachamovitch. "We built IE9 from the ground up for HTML5 and for Windows to deliver the most native HTML5 experience and the best web experience on Windows.

In his keynote two days ago, Hachamovitch claimed: "The only native experience of the web of HTML5 today is on Windows 7 with IE9."

Those comments got an immediate reaction from Mozilla developers, who ridiculed the term in an often-biting entry on Bugzilla, the company's bug- and change-tracking database.

"Mozilla should consider adding support for native HTML5 as well," said Mike Beltzner, a former director of Firefox who recently left Mozilla. "I'm sure that a specification will be produced."

Others quickly chimed in with more satire.

"I'm pretty sure Firefox 5 has 'complete native HTML5' support," said Asa Dotzler, Mozilla's director of community development. "We should resolve this as fixed and be sure to let the world know we beat Microsoft to shipping 'complete' native HTML5."

When some participants in the Bugzilla thread seemed to take Beltzner's call for a Firefox bug fix seriously, Brendan Eich, Mozilla's CTO and the creator of JavaScript, reminded everyone of the joke. "The 'native HTML5' nonsense-phrase is a source of endless fun. Like this bug," said Eich.

Opera was mystified by the phrase too.

"Apropos of 'native HTML5,' I have no idea what it means," said Bruce Lawson, an open-standards evangelist for the Norwegian browser maker and co-author of Introducing HTML5 .

"The beauty of the web is that it's not native to anything. It works on the newest Android phone, any desktop browser and even the ancient Nokia phone a friend of mine in India has," said Lawson. "Even though the native devices are completely different, the thing that unifies them is the web. And HTML5 is the new evolution of the lingua franca of the web."

Haavard Moen, who works in Opera's desktop QA group, was more blunt in his criticism.

In a personal blog post, Moen blasted Hachamovitch. "HTML5 is not native. It is not supposed to be native. It is silly to even attempt to tie HTML5 to a specific platform," Moen wrote. "Hachamovitch should be ashamed of himself for signing his name to such a shoddy piece of dishonest marketing nonsense."

The lack of a clear definition of "native HTML5" forced Lawson and others to speculate on what Hachamovitch meant.

"It could be their attempt to co-opt [the term] 'HTML5' for themselves, and there are many people and organisations that would like to do the same," said Lawson. "But I'm guessing they mean hardware-accelerated HTML5."

If the second is what Microsoft means, it's a continuation of the public relations and marketing effort to cast IE9 - and by extension IE10 - as the best browser for Windows 7. "Microsoft is trying to say that IE9 supports HTML5 natively fast using hardware acceleration only on the latest and greatest OS," said Lawson.

Eich of Mozilla saw it Lawson's way.

"They are talking about performance, or rather the lack of it due to the lack of hardware-accelerated graphics on Windows XP," Eich said on Bugzilla.

But others in the same thread lampooned that definition.

"I don't think general-purpose hardware actually supports 'native HTML5'. Wake me up when we have HTML5 co-processors," said Chris Jones, a web designer and developer who contributes to Firefox.

Microsoft has been beating the drum about browser hardware acceleration since it launched the first public preview of IE9 a year ago. More recently, it has promoted the idea that a browser is only as good as the operating system it runs on, and that by extension, browsers that run on non-Windows OSes, or even on the 10-year-old Windows XP, are sub-standard.

Microsoft has also repeatedly used the phrase "lowest-common denominator" to describe how it sees browser development on XP, Mac and Linux. This week, it applied the same to its four-year-old Windows Vista when it said its next browser, IE10, would not run on that OS.

But the best line came from Beltzner, who first poked Microsoft on Bugzilla.